Support dart and js scripts in HTML tests, on dartium.

tests/html/scripts_test_dart.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library ScriptsTestDart;
+import 'dart:html';
+import 'dart:async';
+
+main() {
+  window.postMessage('squid', '*');
+  window.postMessage('tiger', '*');  // Unexpected message OK.
+  new Timer(new Duration(seconds: 1), () {
+    window.postMessage('squid', '*');  // Duplicate message OK.
+    window.postMessage('sea urchin', '*');
+  });
+}